Method for producing polyurethane emulsion

ABSTRACT

The present invention provides a process for producing a polyurethane emulsion, capable of continuously producing a polyurethane emulsion which contains substantially no organic solvent and also has excellent storage stability over time. Disclosed is a process for producing a polyurethane emulsion by emulsifying a urethane prepolymer, which contains substantially no organic solvent and also has at least two isocyanate groups per one molecule, with water and completing chain extension, the process comprising (1) a first step of supplying the urethane prepolymer and water in an emulsifying apparatus comprising a stator section  5  fixed inside a cylindrical casing  1  and a rotor section  3  fixed to a rotational shaft  2  in the casing  1 , the rotor section  3  having multiple rotor teeth  4 , the stator section  5  having multiple stator teeth  6 , which stand face to face with the rotor teeth  4 , the stator section  5  having an inlet  8  and an outlet  10 , from the inlet  8 , continuously emulsifying them to obtain an emulsion of the urethane prepolymer having an average particle size of 0.1 to 2.5 μm, and discharging the emulsion from the outlet  10 , and (2) a second step of reacting the emulsion of the urethane prepolymer obtained in the first step with a chain extender, thereby completing chain extension of the urethane prepolymer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process for producing apolyurethane emulsion having excellent storage stability by continuouslyemulsifying a urethane prepolymer containing substantially no organicsolvent with water and reacting the urethane prepolymer with a chainextender.

[0003] This application is a continuation of the National Stage ofInternational Application No. PCT/JP03/03627, filed on Mar. 25, 2003,the content of which is incorporated herein by reference. Priority isclaimed on Japanese Patent Application No. 2002-91266, filed Mar. 28,2002, the content of which is incorporated herein by reference.

[0004] 2. Description of Related Art

[0005] In various fields relating to paints, inks, adhesives, textileprocessing and paper processing, polyurethane emulsions are used. Toensure excellent dispersion stability of the polyurethane emulsion, itis required that particles of the polyurethane emulsion have relativelysmall particle size and that dispersed particles of the emulsion areless likely to separate and settle over time and also are superior instorage stability.

[0006] As the process for producing a polyurethane emulsion havingsuperior storage stability, there has been employed a process ofpremixing a urethane prepolymer with water containing an emulsifierusing a simple propeller blade type mixer and finely dispersing theurethane prepolymer under high pressure conditions using a homogenizer.

[0007] When using a urethane prepolymer containing substantially noorganic solvent in such a process, the resulting emulsion containsparticles having relatively large particle size and poor storagestability over time. Therefore, a urethane prepolymer containing acertain amount of an organic solvent (in an amount of about 25 to 60parts by weight based on 100 parts by weight of the solid content of theurethane prepolymer) must be used so as to obtain a polyurethaneemulsion having superior storage stability.

[0008] Thus, it is necessary to perform the step of removing an organicsolvent, which is optionally contained, so as to obtain anenvironmentally friendly polyurethane emulsion containing substantiallyno organic solvent.

[0009] The above process of the prior art had problems in that itrequires numerous steps for fine dispersions and also requires the stepof removing an organic solvent because the organic solvent is contained,resulting in poor production efficiency. Furthermore, the organicsolvent contained in the urethane prepolymer remains in the polyurethaneemulsion.

[0010] To solve these problems, there is proposed a process forcontinuously emulsifying by supplying a mixed solution of a urethaneprepolymer and water in an emulsifying apparatus comprising a rotorsection having multiple rotor teeth fixed to a rotational shaft providedin a cylindrical casing and a stator section having multiple statorteeth, which stand face to face with the rotor teeth, the stator sectionhaving an inlet, (see, for example, Japanese Patent Application, SecondPublication No. Hei 7-68355 (pages 2 to 5)).

[0011] According to this process, an emulsion of a urethane prepolymercomprising fine particles can be obtained by continuously emulsifying acertain urethane prepolymer; however, there cannot be obtained apolyurethane emulsion which contains substantially no organic solventand also has excellent storage stability over time. There is a problemin that the resulting emulsion has poor storage stability when using aurethane prepolymer which has an isocyanate group and has no hydrophilicgroup.

[0012] As the urethane prepolymer, a urethane prepolymer having ahydrophilic group such as ionic group, or a urethane prepolymer whichhas no hydrophilic group or has a very small content of hydrophilicgroup is used according to the purposes, and there is required a processcapable of producing satisfactory polyurethane emulsion even when usingany urethane prepolymer. Among the above urethane prepolymers, as thecontent of the hydrophilic group in the urethane prepolymer increases,the particle size of the polyurethane emulsion obtained byemulsification tends to become small.

[0013] In the above process for continuously emulsifying (see, forexample, Japanese Patent Application, Second Publication No. Hei 7-68355(pages 2 to 5)), when using a urethane prepolymer having no hydrophilicgroup, or a urethane prepolymer having a very small content of thehydrophilic group wherein the content of an ionic group such as anionicgroup or cationic group, as a hydrophilic group, is 0.01 equivalents orless based on 100 parts by weight of the urethane prepolymer, or thecontent of a nonionic hydrophilic group is 5 parts by weight or lessbased on 100 parts by weight of the urethane prepolymer, the particlesize of the emulsion cannot become sufficiently small.

[0014] When using a urethane prepolymer wherein the content of thenonionic hydrophilic group is 10 parts by weight or more based on 100parts by weight of the urethane prepolymer, the particle size can becomesmall to some extent. However, the viscosity of the resultingpolyurethane emulsion increases, and therefore the solid content of thepolyurethane emulsion is limited to about 30% by weight or less and highconcentration polyurethane emulsion cannot be obtained.

[0015] Thus, this process had such a problem that it is impossible tocontinuously produce a polyurethane emulsion which containssubstantially no organic solvent and also has excellent storagestability over time.

SUMMARY OF THE INVENTION

[0016] An object of the present invention is to provide a process forproducing a polyurethane emulsion, capable of continuously producing apolyurethane emulsion which contains substantially no organic solventand also has excellent storage stability over time.

[0017] The present inventors have intensively researched to achieve theabove object and found that, according to the process of the prior art,a urethane prepolymer and water are previously mixed and then suppliedin an emulsifying apparatus in a state of low viscosity (for example, ina coarsely dispersed state where an average particle size of a urethaneprepolymer is from about several tens to several hundreds of microns),and therefore a high shear force is not uniformly applied by the rotorteeth rotating at high speed and it is not easy to obtain a finelydispersed emulsion of an urethane prepolymer, resulting in poor storagestability over time.

[0018] Consequently, it has been made clear that, by supplying aurethane prepolymer and water in an emulsifying apparatus withoutpreviously dispersing them with each other, a high shear force can beuniformly applied to the urethane prepolymer by the rotor teeth rotatingat high speed and an emulsion of a urethane prepolymer having a fineparticle size can be continuously produced.

[0019] Furthermore, it has been found that a polyurethane emulsionhaving excellent storage stability can be continuously produced by usinga urethane prepolymer, which contains substantially no organic solventand also has at least two isocyanate groups per one molecule,emulsifying the urethane prepolymer with water to obtain an emulsion ofthe urethane prepolymer having an average particle size of 0.1 to 2.5μm, and continuously reacting the emulsion with a chain extender,thereby completing chain extension of the urethane prepolymer. Thus, thepresent invention has been completed.

[0020] That is, the present invention provides a process for producing apolyurethane emulsion by emulsifying a urethane prepolymer, whichcontains substantially no organic solvent and also has at least twoisocyanate groups per one molecule, with water and completing chainextension, the process comprising:

[0021] (1) a first step of supplying the urethane prepolymer and waterfrom a inlet into an emulsifying apparatus comprising a stator sectionfixed inside a cylindrical casing and a rotor section fixed to arotational shaft in the casing, the rotor section having multiple rotorteeth, the stator section having multiple stator teeth, which stand faceto face with the rotor teeth, the stator section having the inlet and anoutlet, continuously emulsifying them to obtain an emulsion of theurethane prepolymer having an average particle size of 0.1 to 2.5 μm,and discharging the emulsion from the outlet, and

[0022] (2) a second step of reacting the emulsion of the urethaneprepolymer obtained in the first step with a chain extender, therebycompleting chain extension of the urethane prepolymer.

[0023] According to the process for producing a polyurethane emulsion ofthe present invention, it is made possible to eliminate the step ofremoving an organic solvent and to continuously produce a polyurethaneemulsion which contains substantially no organic solvent and an averageparticle size within a range from 0.1 to 2.5 μm, and also has excellentstorage stability.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic view showing an emulsifying apparatus usedin the present invention.

[0025]FIG. 2 is a sectional side view showing a rotor section 3 and astator section 5 of an emulsifying apparatus used in the presentinvention.

[0026]FIG. 3 is a sectional view taken along lines A-A in FIG. 2 of therotor section 3 of the emulsifying apparatus used in the presentinvention. In FIG. 3, comb-shaped teeth 5 a on the stator and slits 5 bbetween the comb-shaped teeth on the stator are omitted. Also thesection of a casing 1 is omitted.

[0027]FIG. 4 is a sectional view taken along lines B-B in FIG. 2 of thestator section 5 of the emulsifying apparatus used in the presentinvention. In FIG. 4, comb-shaped teeth 3 a on the rotor and slits 3 bbetween the comb-shaped teeth on the rotor are omitted. Also the sectionof a casing 1 is omitted.

[0028]FIG. 5 is a schematic view showing a liquid feed line of aproduction process of an emulsion of a urethane prepolymer produced inthe present invention.

[0029]FIG. 6 is a sectional side view showing a rotor section 17 and astator section 19 of an emulsifying apparatus of the prior art.

[0030]FIG. 7 is a schematic view showing a liquid feed line of anemulsifying apparatus of the prior art.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will now be described in detail.

[0032] The process for producing a polyurethane emulsion of the presentinvention comprises supplying a urethane prepolymer, which containssubstantially no organic solvent and also has at least two isocyanategroups per one molecule, and water in a specific emulsifying apparatus,continuously emulsifying the urethane prepolymer with water to obtain anemulsion of the urethane prepolymer having an average particle size of0.1 to 2.5 μm, and continuously reacting the emulsion with a chainextender, thereby completing chain extension of the urethane prepolymer.

[0033] The specific emulsifying apparatus used in the present inventionwill now be described in detail.

[0034] As shown in FIG. 1 and FIG. 2, the emulsifying apparatus used inthe present invention may have a structure comprising a stator section 5having multiple stator teeth 6 fixed inside a cylindrical casing 1 and arotor section 3 having multiple rotor teeth 4 fixed to a rotationalshaft 2 in the casing 1, the stator section 5 having at least two inlets8. At least two inlets 8 are preferably provided. Multiple rotor teeth 4can be rotated at high speed by the rotation of the rotational shaft 2.

[0035] At least two inlets 8 are preferably provided. By providing thestator section 5 with at least two inlets 8, it becomes easier to supplythe urethane prepolymer and water in the emulsifying apparatus withoutmutually mixing them. By employing this structure, the urethaneprepolymer and water can be separately supplied from two inlets 8 andtherefore a shear force can be applied under proper viscosity justbefore the urethane prepolymer is dispersed in water, thus making itpossible to form more fine particles.

[0036] Three or more inlets 8 can also be provided. In this case,emulsifiers or other additives can be charged from an inlet 8 differentfrom those used to charge water and urethane prepolymer, in addition tothe urethane prepolymer and water, and then be uniformly mixed.

[0037] As shown in FIG. 5, the urethane prepolymer and water arecontinuously supplied from the inlet 8 of the stator section 5 by twopumps 13 which are separately connected to a urethane prepolymerreaction vessel 11 and a water tank 12.

[0038] An outer diameter of the rotor section 3 and the stator section 5can be optionally selected and a peripheral velocity of the outermostperiphery is decided by a combination of an outer diameter L of therotor and a rotational velocity R of the rotor section 3. A peripheralvelocity X of a rotor tooth at the outermost periphery among multiplerotor teeth 4 is preferably within a range from 30 to 70 m/s, and morepreferably from 40 to 60 m/s. When the peripheral velocity X of therotor tooth at the outermost periphery is within the above range, therecan be obtained a shear force which is sufficiently effective foremulsification.

[0039] The peripheral velocity X (unit: m/s) of the rotor tooth at theoutermost periphery can be calculated from a value of an outer diameterL (unit: m) of the rotator and a value of a rotational velocity R (unit:rpm) based on the following equation [1].

X=ΠL×(R/60)   Equation (1)

[0040] According to the equation [1], when the outer diameter of therotor is 13 cm and the rotational velocity is 6000 rpm, the peripheralvelocity X of the rotor tooth at the outermost periphery is 40.8 m/s.

[0041] As shown in FIG. 2, FIG. 3 and FIG. 4, the stator section 5 isprovided with at least two generally ring-shaped stator teeth 6 and therotor section 3 is provided with at least two generally ring-shapedrotor teeth 4 inside the stator teeth 6. The rotor teeth 4 and thestator teeth 6 are respectively provided with multiple comb-shaped teeth3 a and multiple comb-shaped teeth 5 a in a circumferential direction.Between the comb-shaped teeth 3 a on the rotor teeth 4 and between thecomb-shaped teeth 5 a on the stator teeth 6, slits 3 b and slits 5 b arerespectively provided. In FIG. 3, the comb-shaped teeth 5 a on thestator teeth 6, and the slits 5 b between the comb-shaped teeth on thestator teeth are omitted. In FIG. 4, the comb-shaped teeth 3 a on therotor teeth 4, and the slits 3 b between the comb-shaped teeth on therotor teeth are omitted. In FIG. 3 and FIG. 4, the section of a casing 1is omitted.

[0042] With respect to the width of these slits 3 b and slits 5 b(hereinafter referred to as a slit width), the slit width is preferablyreduced so that the average particle size of the resulting polyurethaneemulsion becomes small in the case of the stator and rotor located atthe outer side, and a slit width at the inner side is preferably withina range from 3 to 10 mm and a slit width at the outermost periphery ispreferably within a range from 0.1 to 1.0 mm.

[0043] Between the rotor teeth 4 and the stator teeth 6, a clearance 15is provided and the width of the clearance 15 is preferably within arange from 100 to 1000 μm, and more preferably from 100 to 500 μm. Whenthe width of the clearance 15 between the rotor teeth 4 and the statorteeth 6 is within the above range, a polyurethane emulsion having fineparticles can be obtained.

[0044] The emulsifying apparatus used in the present invention has aspace section 7 surrounded by the rotor section 3 and the stator section5 in the vicinity of a rotational shaft. In the vicinity of therotational shaft of the space section 7, since the urethane prepolymerand water charged in the casing 1 easily moves rapidly in acircumferential direction by a centrifugal force due to the rotation ofthe rotor section 3, it is preferable to provide a blade 9 inside therotor section 3.

[0045] In the first step of the process for producing a polyurethaneemulsion according to the present invention, a urethane prepolymer andwater are supplied from the inlet 8 of the emulsifying apparatus havingthe above-described feature and then continuously emulsified whileapplying a high shear force to the urethane prepolymer and water.

[0046] First, a urethane prepolymer, which substantially contains noorganic solvent and also has at least two isocyanate groups per onemolecule, and water flow into a space section 7 from the inlet 8 andsimultaneously flow into a clearance between the rotor teeth 4 and thestator teeth 6 located at a first stage in a centrifugal direction froma central axis of the rotation by a centrifugal force produced byrotating the rotor section 3 at high speed, and then pass throughmultiple slits 3 b and multiple slits 5 b of the rotor teeth 4 and thestator teeth 6.

[0047] The urethane prepolymer and water flow into a clearance betweenthe rotor teeth 4 and the stator teeth 6 located at a second stage in acentrifugal direction from a central axis of the rotation, and then ashear force based on velocity gradient of the rotor teeth 4 in atangential direction is applied on the urethane prepolymer, and thus theurethane prepolymer is dispersed in water.

[0048] The step of passing the urethane prepolymer and water throughmultiple slits 3 b and multiple slits 5 b of the rotor teeth 4 and thestator teeth 6 and applying a shear force based on velocity gradient ofthe rotor teeth 4 is sequentially repeated at high speed, and thus theurethane prepolymer is finely dispersed in water and then an emulsion ofthe urethane prepolymer having an average particle size of 0.1 to 2.5 μmis discharged from an outlet 10.

[0049] In the second step, the emulsion of the urethane prepolymerobtained in the first step is reacted with a chain extender, therebycompleting chain extension of the urethane prepolymer, thus making itpossible to continuously produce a polyurethane emulsion.

[0050] Although it is not required to apply a pressure in theemulsifying apparatus, a back pressure of about 1 to 3 kg/cm² ispreferably applied for the stable operation of the emulsifying apparatuswithout causing cavitation.

[0051] A flow rate of the urethane prepolymer and water, into theemulsifying apparatus, is preferably from 0.1 to 4 m³ per hour, and isparticularly preferably from 0.5 to 2 m³ per hour, in view ofproductivity.

[0052] When the urethane prepolymer is supplied in the emulsifyingapparatus, the urethane prepolymer is necessary to heat until gettingappropriate fluidity so as to adjust the viscosity of the urethaneprepolymer to the viscosity suited for emulsification.

[0053] The methods for adjusting the viscosity of the urethaneprepolymer includes addition of a chemical agent having low activitywith an isocyanate group of the urethane prepolymer or a chemical agenthaving no reactive group, for example, chemical agents having lowviscosity, such as plasticizer, and epoxy diluent.

[0054] A mixing ratio of the urethane prepolymer to the total weight ofthe urethane prepolymer and water to be supplied in the emulsifyingapparatus varies depending on the viscosity of the urethane prepolymerto be supplied in the emulsifying apparatus. To obtain an emulsionhaving fine particles, when the urethane prepolymer has a hydrophilicgroup, the content of the urethane prepolymer having a hydrophilic groupis preferably within a range from 30 to 50% by weight. When the urethaneprepolymer has no hydrophilic group, the content of the urethaneprepolymer having no hydrophilic group is preferably within a range from50 to 90% by weight.

[0055] After emulsifying at the above mixing ratio of the urethaneprepolymer to the total weight of the urethane prepolymer and water, theresulting emulsion can be optionally diluted by further additionalwater.

[0056] The urethane prepolymer used in the present invention will now bedescribed.

[0057] The urethane prepolymer used in the present invention is aurethane prepolymer which contains substantially no organic solvent andalso has at least two isocyanate groups per one molecule. Such aurethane prepolymer refers to a urethane prepolymer wherein the contentof the organic solvent in the urethane prepolymer is 10% by weight orless. To eliminate the step of removing the organic solvent, the contentof the organic solvent is preferably 5% by weight or less, morepreferably 1% by weight or less, and most preferably 0.1% by weight orless.

[0058] The number average molecular weight of the urethane prepolymerused in the present invention is preferably within a range from 1,000 to20,000.

[0059] The urethane prepolymer used in the present invention can beproduced by a conventionally known process, for example, a process forreacting a polyisocyanate compound with an active hydrogen-containingcompound and examples thereof include 1) a process for reacting apolyisocyanate compound described hereinafter with a polyol compounddescribed hereinafter without using an organic solvent, and 2) a processfor reacting a polyisocyanate compound described hereinafter with apolyol compound described hereinafter in an organic solvent, followed byremoval of the solvent. Among these processes, the former process ispreferable because the step of removing the solvent is not required.

[0060] In the above reaction, the polyisocyanate compound is reactedwith the active hydrogen-containing compound at a temperature ofpreferably from 20 to 120° C., and more preferably 30 to 100° C. at anequivalent ratio of an isocyanate group to an active hydrogen group ofpreferably from 1.1:1 to 3:1, and more preferably from 1.2:1 to 2:1.

[0061] In the reaction, an excess isocyanate group is optionally reactedwith aminosilane, thereby converting the terminal group into a reactivegroup other than isocyanate group, such as an alkoxysilyl group.

[0062] Examples of the polyisocyanate compound include 2,4-tolylenediisocyanate, 2,6-tolylene diisocyanate, m-phenylene diisocyanate,p-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate,2,4′-diphenylmethane diisocyanate, 2,2′-diphenylmethane diisocyanate,3,3′-dimethyl-4,4′-biphenylene diisocyanate,3,3′-dimethoxy-4,4′-biphenylene diisocyanate,3,3′-dichloro-4,4′-biphenylene diisocyanate, 1,5-naphthalenediisocyanate, 1,5-tetrahydronaphthalene diisocyanate, tetramethylenediisocyanate, 1,6-hexamethylene diisocyanate, dodecamethylenediisocyanate, trimethylhexamethylene diisocyanate, 1,3-cyclohexylenediisocyanate, 1,4-cyclohexylene diisocyanate, xylylene diisocyanate,tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate,lysine diisocyanate, isophorone diisocyanate, 4,4′-dicyclohexylmethanediisocyanate, and 3,3′-dimethyl-4,4′-dicyclohexylmethane diisocyanate.

[0063] The active hydrogen-containing compound used to produce theurethane prepolymer used in the present invention includes, for example,a compound having comparatively high molecular weight (hereinafterreferred to as a high-molecular weight compound) and a compound havingcomparatively low molecular weight (hereinafter referred to as alow-molecular weight compound).

[0064] The number average molecular weight of the high-molecular weightcompound is preferably within a range from 300 to 10,000, and morepreferably from 500 to 5,000. The number average molecular weight of thelow-molecular weight compound is less than 300.

[0065] These active hydrogen-containing compounds may be used alone, ortwo or more kinds of them may be used in combination.

[0066] Among these active hydrogen-containing compounds, examples of thehigh-molecular weight compound include polyester polyol, polyetherpolyol, polycarbonate polyol, polyacetal polyol, polyacrylate polyol,polyesteramide polyol, polythioether polyol, polyolefin polyols such aspolybutadiene polyol, and so on.

[0067] As the polyester polyol, polyester polyol obtained by thepolycondensation reaction of a glycol described hereinafter and an aciddescribed hereinafter can be used.

[0068] Examples of the glycol, which can be used to obtain the polyesterpolyol, include ethylene glycol, propylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol,1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, polyethylene glycol (molecular weight: 300 to6,000), dipropylene glycol, tripropylene glycol,bishydroxyethoxybenzene, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,bisphenol A, hydrogenated bisphenol A, hydroquinone, and alkylene oxideadducts thereof.

[0069] Examples of the acid, which can be used to obtain the polyesterpolyol, include succinic acid, adipic acid, azelaic acid, sebacic acid,dodecanedicarboxylic acid, maleic anhydride, fumaric acid,l,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid,terephthalic acid, isophthalic acid, phthalic acid,1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylicacid, 1,2-bis(phenoxy)ethane-p,p′-dicarboxylic acid, and anhydrides orester-forming derivatives of these dicarboxylic acids; andp-hydroxybenzoic acid, p-(2-hydroxyethoxy)benzoic acid, andester-forming derivatives of these hydroxycarboxylic acids.

[0070] Also a polyester obtained by the ring-opening polymerizationreaction of a cyclic ester compound such as ε-caprolactone, andcopolyesters thereof can be used.

[0071] Examples of the polyether polyol include compounds obtained bythe polyaddition reaction of one or more kinds of compounds having atleast two active hydrogen atoms such as ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, trimethylene glycol,1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol,glycerin, trimethylolethane, trimethylolpropane, sorbitol, sucrose,aconite saccharide, trimellitic acid, hemimellitic acid, phosphoricacid, ethylenediamine, diethylenetriamine, triisopropanolamine,pyrogallol, dihydroxybenzoic acid, hydroxyphthalic acid, and1,2,3-propanetrithiol with one or more kinds among ethylene oxide,propylene oxide, butylene oxide, styrene oxide, epichlorohydrin,tetrahydrofuran, and cyclohexylene.

[0072] Examples of the polycarbonate polyol include compounds obtainedby the reaction of glycols such as 1,4-butanediol, 1,6-hexanediol, anddiethylene glycol, with diphenyl carbonate and phosgene.

[0073] Among the active hydrogen-containing compounds, the low-molecularweight compound is a compound which has at least two active hydrogensper one molecule and has a number average molecular weight of less than300 and examples thereof include glycol components used as raw materialsof the polyester polyol; polyhydroxy compounds such as glycerin,trimethylolethane, trimethylolpropane, sorbitol, and pentaerythritol;and amine compounds such as ethylenediamine, 1,6-hexamethylenediamine,piperazine, 2,5-dimethylpiperazine, isophoronediamine,4,4′-dicyclohexylmethanediamine,3,3′-dimethyl-4,4′-dicyclohexylmethanediamine, 1,4-cyclohexanediamine,1,2-propanediamine, hydazine, diethylenetriamine, andtriethylenetetramine.

[0074] The average particle size of the polyurethane emulsion obtainedin the present invention varies depending on the presence or absence ofa hydrophilic group or the content of a hydrophilic group in theurethane prepolymer to be used. The average particle size of thepolyurethane emulsion obtained by using the urethane prepolymer having ahydrophilic group is smaller than that in case of using the urethaneprepolymer having no hydrophilic group.

[0075] Specifically, the hydrophilic group means an ionic group such asan anionic group (for example, carboxyl group, sulfonic acid group, orphosphoric acid group) or a cationic group (for example, tertiary aminogroup, or quaternary amino group), or a nonionic hydrophilic group (forexample, a group composed of a repeating unit of ethylene oxide, or agroup composed of a repeating unit of ethylene oxide and a repeatingunit of another alkylene oxide).

[0076] The polyurethane emulsion having a smaller average particle sizeis preferable and has excellent storage stability.

[0077] When the urethane prepolymer has a hydrophilic group, a finelydispersed polyurethane emulsion having an average particle size of about0.1 to 1.0 μm can be obtained and has excellent storage stability.Therefore, the resulting polyurethane emulsion is suited to various usessuch as paints, inks, pigment vehicles, adhesives, and primers ofplastic film.

[0078] When the resulting polyurethane emulsion is used in combinationwith other kinds of emulsions and other chemicals for various purposessuch as textile processing, paper processing, and glass fiber binder, aurethane prepolymer having an ionic group such as an anionic group orcationic group is not preferably used because a polyurethane emulsionhaving an anionic or cationic hydrophilic group is likely to agglomerateand settle in mixing.

[0079] In these purposes, therefore, a urethane prepolymer having noionic group, a urethane prepolymer having a very small content of anionic group, and a urethane prepolymer having a nonionic hydrophilicgroup such as polyoxyethylene chain are preferably used.

[0080] The urethane prepolymer having a very small content of an ionicgroup is specifically a urethane prepolymer wherein the content of theionic group such as an anionic group or cationic group is 0.01equivalents or less based on 100 parts by weight of the urethaneprepolymer.

[0081] When the content of the nonionic hydrophilic group exceeds 20parts by weight based on 100 parts by weight of the urethane prepolymer,the particle size can become small but the resulting polyurethaneemulsion has high viscosity, and therefore the solid content of thepolyurethane emulsion is limited within a range from about 20 to 30% byweight and it is not preferable according to the purposes. In practice,the content of the nonionic hydrophilic group is preferably controlledto 20 parts by weight or less, and more preferably 10 parts by weight orless, based on 100 parts by weight of the urethane prepolymer.

[0082] Even when using any type of urethane prepolymers described above,according to the present invention, dispersed particles having anaverage particle size within a range from 0.1 to 2.5 μm are less likelyto separate and settle over time and a polyurethane emulsion havingexcellent storage stability can be obtained.

[0083] In the present invention, according to the purposes, a urethaneprepolymer having an ionic group such as anionic group or cationicgroup, or a urethane prepolymer having a hydrophilic group such asnonionic hydrophilic group can be used, as described above. In thiscase, an emulsion having a small average particle size can be obtained.

[0084] Among hydrophilic groups, a nonionic hydrophilic group having arepeating unit of ethylene oxide is preferable because the finallyobtained polyurethane emulsion has excellent compatibility with otherkinds of emulsions. Introduction of a carboxyl group and/or a sulfonicacid group is effective to make the particle size finer.

[0085] The ionic group refers to a functional group capable of servingas a hydrophilic ionic group which contributes to self dispersibility inwater by neutralization.

[0086] When the ionic group is an anionic group, the neutralizer usedfor neutralization includes, for example, nonvolatile bases such assodium hydroxide and potassium hydroxide; and volatile bases such astertiary amines (e.g. trimethylamine, triethylamine,dimethylethanolamine, methyldiethanolamine, and triethanolamine) andammonia can be used.

[0087] When the ionic group is a cationic group, usable neutralizerincludes, for example, inorganic acids such as hydrochloric acid,sulfuric acid, and nitric acid; and organic acids such as formic acidand acetic acid.

[0088] Neutralization may be conducted before, during or after thepolymerization of the compound having an ionic group. Alternatively,neutralization may be conducted during or after the urethanepolymerization reaction.

[0089] To introduce a hydrophilic group in the urethane prepolymer, acompound, which has at least one active hydrogen atom per one moleculeand also has the above hydrophilic group, may be used as an activehydrogen-containing compound.

[0090] Examples of the compound, which has at least one active hydrogenatom per one molecule and also has the above hydrophilic group, includesulfonic acid group-containing compounds such as 2-oxyethanesulfonicacid, phenolsulfonic acid, sulfobenzoic acid, sulfosuccinic acid,5-sulfoisophthalic acid, sulfanilic acid,1,3-phenylenediamine-4,6-disulfonic acid, and2,4-diaminotoluene-5-sulfonic acid, and derivatives thereof, orpolyester polyols obtained by copolymerizing them;

[0091] carboxylic acid-containing compounds such as2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid,2,2-dimethylolvaleric acid, dioxymaleic acid, 2,6-dioxybenzoic acid, and3,4-diaminobenzoic acid, and derivatives thereof, or polyester polyolsobtained by copolymerizing them; tertiary amino group-containingcompounds such as methyldiethanolamine, butyldiethanolamine, andalkyldiisopropanolamine, and derivatives thereof, or polyester polyol orpolyether polyol obtained by copolymerizing them;

[0092] reaction products of the above tertiary amino group-containingcompounds, or derivatives thereof, or polyester polyols or polyetherpolyols obtained by copolymerizing them, with quaternizing agents suchas methyl chloride, methyl bromide, dimethylsulfuric acid,diethylsulfuric acid, benzyl chloride, benzyl bromide,ethylenechlorohydrin, ethylenebromohydrin, epichlorohydrin, andbromobutane; and

[0093] nonionic group-containing compounds such as polyoxyethyleneglycol or polyoxyethylene-polyoxypropylene copolymer glycol, which hasat least 30% by weight of a repeating unit of ethylene oxide and atleast one active hydrogen in the polymer and also has a molecular weightof 300 to 20,000, polyoxyethylene-polyoxybutylene copolymer glycol,polyoxyethylene-polyoxyalkylene copolymer glycol, and monoalkyl etherthereof, or polyester-polyether polyols obtained by copolymerizing them.

[0094] These compounds can be used alone, or two or more kinds of themcan be used in combination.

[0095] When the urethane prepolymer has a hydrophilic group in themolecule, water used in the present invention may not contain anemulsifier. On the other hand, when the urethane prepolymer has nohydrophilic group, water must contain an emulsifier so as to improve thestorage stability of the polyurethane emulsion by finely dispersing theurethane prepolymer in water.

[0096] Examples of the emulsifier include nonionic emulsifiers such aspolyoxyethylene-polyoxypropylene copolymer, polyoxyethylene nonylphenylether, polyoxyethylene lauryl ether, polyoxyethylene styrenated phenylether, and polyoxyethylene sorbitol tetraoleate;

[0097] anionic emulsifiers such as fatty acid salt (e.g. sodium oleate),alkyl sulfate ester salt, alkylbenzene sulfonate, alkyl sulfosuccinate,naphthalene sulfonate, alkane sulfonate sodium salt, and sodiumalkyldiphenyl ether sulfonate; and

[0098] nonionic anionic emulsifiers such as polyoxyethylene alkylsufonate, and polyoxyethylene alkyl phenyl sulfonate.

[0099] The amount of the emulsifier is preferably within a range from0.1 to 15 parts by weight, and more preferably from 1 to 10 parts byweight, based on 100 parts by weight of the urethane prepolymer.

[0100] The urethane prepolymer used in the present invention ispreferably liquid at normal temperature, or has high viscosity at normaltemperature, or is solid at normal temperature but has a viscosity of200 to 10,000 mPa.s at a temperature higher than a melting point in viewof high efficiency of emulsification by high shear force using anemulsifying apparatus and good processability.

[0101] In the process for producing polyurethane emulsion of the presentinvention, aqueous dispersions and stabilizers can be optionally addedto water. Examples of the aqueous dispersion include emulsions ofpolyvinyl acetate, polyethylene-vinyl acetate, polyacrylic, andpolyacrylic-styrenic; latexes of polystyrene-butadiene,polyacrylonitrile-butadiene, and polyacrylic-butadiene; aqueousdispersions of polyethylene and polyolefin ionomers; and various aqueousdispersions of polyurethane, polyester, polyamide, and epoxy resin.

[0102] In the first step of the present invention, an emulsion of aurethane prepolymer having an average particle size of 0.1 to 2.5 μm isfirst obtained.

[0103] In the second step of the present invention, the emulsion of theurethane prepolymer obtained in the first step is reacted with a chainextender, thereby to complete chain extension of the urethaneprepolymer, thus making it possible to continuously produce apolyurethane emulsion having excellent storage stability.

[0104] Examples of the chain extender used in the present inventioninclude water; diamines such as ethylenediamine, 1,2-propanediamine,1,6-hexamethylenediamine, piperazine, 2-methylpiperazine,2,5-dimethylpiperazine, isophoronediamine,4,4′-dicyclohexylmethanediamine,3,3′-dimethyl-4,4′-dicyclohexylmethanediamine, 1,2-cyclohexanediamine,1,4-cyclohexanediamine, aminoethylethanolamine, aminopropylethanolamine,aminohexylethanolamine, aminoethylpropanolamine,aminopropylpropanolamine, and aminohexylpropanolamine; polyamines suchas diethylenetriamine, dipropylenetriamine, and triethylenetetramine;hydrazines; acid hydrazides. These chain extenders can be used alone orin combination.

[0105] According to the present invention, the step of removing theorganic solvent can be eliminated and a polyurethane emulsion, whichcontains emulsion particles having a very small average particle sizeand has excellent storage stability, can be provided even when using aurethane prepolymer having no hydrophilic group, or a urethaneprepolymer having a very small content of the hydrophilic group.

EXAMPLES

[0106] The present invention will be described in detail by way ofexamples. In the following examples, parts are by weight unlessotherwise specified.

[0107] The measurement of the average particle size and the evaluationof storage stability are conducted by the following methods. [Method formeasurement of average particle size]

[0108] Using the polyurethane emulsions obtained in Examples andComparative Examples as samples, the average particle size was measuredby a laser diffraction particle size analyzer “SALD-2100” manufacturedby Shimadzu Corporation. The value of the average particle size is amedian size on a volume basis (particle size at which the cumulativedistribution of particles becomes 50%).

[0109] [Method for Evaluation of Storage Stability]

[0110] The polyurethane emulsion was diluted to obtain a solution havinga concentration of 20% by weight, which was charged in a test tube andallowed to stand. After one day had passed, the state of settlement wasvisually observed. A volume ratio of a transparent supernatant portionto the entire solution was visually measured and the storage stabilitywas evaluated.

[0111] The results are shown in Table 1. The smaller “supernatantamount” as the volume ratio of the supernatant portion exhibits smallersettling rate and better storage stability.

Example 1

[0112] 1000 Parts of polyoxypropylene glycol having a molecular weightof 1,000, 82.2 parts of dimethylolpropionic acid and 628.0 parts ofisophorone diisocyanate were reacted at 90° C. in the presence of 0.2parts of stannous octoate until the isocyanate group content reached6.0% by weight to obtain a terminated isocyanate group-containingurethane prepolymer A (viscosity at 70° C.: 900 mPa.s, isocyanate groupcontent: 6.0% by weight, carboxyl group content: 0.035 equivalents basedon 100 parts by weight).

[0113] The urethane prepolymer A heating at 70° C. and water containingtriethylamine, as a neutralizer, in an amount of 0.024 equivalents basedon 100 parts by weight of water were simultaneously supplied in anemulsifying apparatus shown in FIG. 2 from separate inlets 8 of theemulsifying apparatus at a rate of 0.2 m³ per hour (prepolymer) and arate of 0.3 m³ per hour (water).

[0114] An emulsification treatment was conducted at a peripheralvelocity of a rotor section 3 of the emulsifying apparatus of 40 m/s tocontinuously obtain an emulsion of a urethane prepolymer having anaverage particle size of 0.18 μm shown in Table 1 at a rate of 0.5 m³per hour.

[0115] Immediately after the emulsification treatment, a solutionprepared by diluting hydrazine with water, which has an amino group inthe amount corresponding to 90% of an isocyanate group, was added,thereby completing chain extension, thus yielding a polyurethaneemulsion having a solid content of 35% by weight.

[0116] An emulsifying apparatus, in which a rotor section 3 has adiameter of 130 mm, a clearance between rotor teeth 4 and stator teeth 6is 250 μm, and a slit width of a rotor tooth at the outermost peripheryis 0.4 mm, was used.

Example 2

[0117] 1000 Parts of polyoxypropylene glycol having a molecular weightof 650 and 675.0 parts of isophorone diisocyanate were reacted at 90° C.in the presence of 0.2 parts of stannous octoate until the isocyanategroup content reached 7.5% by weight to obtain a terminated isocyanategroup-containing urethane prepolymer B (viscosity at 70° C.: 1000 mPa.s,isocyanate group content: 7.5% by weight).

[0118] The urethane prepolymer B heating at 70° C. and water containing10% by weight of a polyoxyethylene-polyoxypropylene copolymer, as anemulsifier, were simultaneously supplied in an emulsifying apparatusshown in FIG. 2 from separate inlets 8 of the emulsifying apparatus at arate of 0.2 m³ per hour (prepolymer) and a rate of 0.15 m³ per hour(water).

[0119] An emulsification treatment was conducted at a peripheralvelocity of a rotor section 3 of the emulsifying apparatus of 49 m/s tocontinuously obtain an emulsion of a urethane prepolymer having anaverage particle size of 2.4 μm shown in Table 2 at a rate of 0.35 m³per hour. Immediately after the emulsification treatment, a solutionprepared by diluting hydazine with water, which has an amino group inthe amount corresponding to 90% of an isocyanate group, was added,thereby completing chain extension, thus yielding a polyurethaneemulsion having a solid content of 50% by weight.

[0120] The same emulsifying apparatus as in Example 1 was used.

[0121] Comparative Example 1

[0122] In place of the emulsifying apparatus shown in FIG. 2 used inExample 2, an emulsifying apparatus comprising a stator section 19having an inlet 22 shown in FIG. 6 was used. In FIG. 6, the referencesymbol 16 denotes a rotational shaft, the reference symbol 17 denotes arotor section, the reference symbol 18 denotes rotor teeth, thereference symbol 20 denotes stator teeth, the reference symbol 21denotes a space section, and the reference symbol 23 denotes an outlet.The same urethane prepolymer and water containing the emulsifier asthose used in Example 2 were previously mixed by using a stirrer and themixed solution was charged in an emulsifying apparatus at a rate of 0.35m³ per hour, and then an emulsification treatment was conducted at aperipheral velocity of a rotor section 3 of the emulsifying apparatus of49 m/s. As a result, an average particle size of the resulting emulsionof the urethane prepolymer was 3.4 μm as shown in Table 2 and theurethane prepolymer is not finely dispersed. Immediately after theemulsification treatment, a solution prepared by diluting hydrazine withwater, which has an amino group in the amount corresponding to 90% of anisocyanate group, was added, thereby completing chain extension, thusyielding a polyurethane emulsion having a solid content of 50% byweight. The supernatant amount was 65% and the resulting emulsion wasdrastically inferior in storage stability as compared to Example 2.

[0123] Comparative Example 2

[0124] In place of the emulsifying apparatus shown in FIG. 2 used inExample 2, an emulsifying apparatus comprising a stator section 19having an inlet 22 shown in FIG. 6 was used. Without previously mixing,a urethane prepolymer and water containing an emulsifier were charged inan inlet at a rate of 0.2 m³ per hour (urethane prepolymer) and a rateof 0.15 m³ per hour (aqueous emulsifier solution) using a liquid feedline of the emulsifying machine, in which flows of the urethaneprepolymer and water meet at a mixing section 29 located right beforethe emulsifying machine, as shown in FIG. 7. In FIG. 7, the referencesymbol 24 denotes a casing of the emulsifying machine, the referencesymbol 25 denotes a urethane prepolymer reaction vessel, the referencesymbol 26 denotes a water tank, the reference symbol 27 denotes a pump,and the reference symbol 28 denotes a product tank. An emulsificationtreatment was conducted at a peripheral velocity of a rotor section 3 ofthe emulsifying apparatus of 49 m/s. As a result, an average particlesize of the resulting emulsion of the urethane prepolymer was 3.3 μm asshown in Table 2 and the urethane prepolymer is not finely dispersed.Immediately after the emulsification treatment, a solution prepared bydiluting hydrazine with water, which has an amino group in the amountcorresponding to 90% of an isocyanate group, was added, therebycompleting chain extension, thus yielding a polyurethane emulsion havinga solid content of 50% by weight. The supernatant amount was 55% and theresulting emulsion was drastically inferior in storage stability ascompared to Example 2. TABLE 1 Example 1 Average particle 0.18 size (μm)

[0125] TABLE 2 Comparative Comparative Example 2 Example 1 Example 2Average particle 2.4 3.4 3.3 size (μm) Supernatant 21 65 55 amount (%)

What is claimed is:
 1. A process for producing a polyurethane emulsionby emulsifying a urethane prepolymer, which contains substantially noorganic solvent and also has at least two isocyanate groups per onemolecule, with water and then completing chain extension, the processcomprising: (1) a first step of supplying the urethane prepolymer andwater in an emulsifying apparatus comprising a stator section 5 fixedinside a cylindrical casing 1 and a rotor section 3 fixed to arotational shaft 2 in the casing 1, the rotor section 3 having multiplerotor teeth 4, the stator section 5 having multiple stator teeth 6,which stand face to face with the rotor teeth 4, the stator section 5having an inlet 8 and an outlet 10, from the inlet 8, continuouslyemulsifying them to obtain an emulsion of the urethane prepolymer havingan average particle size of 0.1 to 2.5 μm, and discharging the emulsionfrom the outlet 10, and (2) a second step of reacting the emulsion ofthe urethane prepolymer obtained in the first step with a chainextender, thereby completing chain extension of the urethane prepolymer.2. The process for producing a polyurethane emulsion according to claim1, wherein the emulsifying apparatus has at least two inlets 8 in thestator section 5 and the urethane prepolymer and water are supplied inthe emulsifying apparatus from separate inlets
 8. 3. The process forproducing a polyurethane emulsion according to claim 1, wherein aperipheral velocity of the rotor tooth located at the outermostperiphery among multiple rotor teeth 4 of the emulsifying apparatus iswithin a range from 30 to 70 m/second.
 4. The process for producing apolyurethane emulsion according to claim 1, wherein a clearance 15between the rotor teeth 4 and the stator teeth 6 of the emulsifyingapparatus is within a range from 100 to 500 μm.
 5. The process forproducing a polyurethane emulsion according to claim 1, wherein a blade9 is provided in a space section 7 surrounded by the rotor section 3 andthe stator section 5 of the emulsifying apparatus.